1. Field of the Invention
The present invention relates to a method and an apparatus for classifying defects of an object. More particularly, the present invention relates to a method and an apparatus for rapidly inspecting and classifying defects, such as particles or scratches, of an object, such as a wafer.
2. Description of the Related Art
A semiconductor fabricating process indispensably requires a process for inspecting defects of an object, such as a wafer. For example, after forming fine patterns on the wafer using a photolithography process, defects, such as particles or micro-scratches, may be generated on the pattern formed on the wafer. In addition, when a chemical mechanical polishing (CMP) process is performed on the wafer including the patterns, additional defects may be generated on the pattern formed on the wafer.
Conventional inspection equipment may inspect only whether defects are present on the patterns. Conventionally, an inspector directly identifies defects either by the naked eye or by using an additional review tool.
As inspection equipment has rapidly improved, an ability to manage scores of defects has improved to an ability to manage hundreds or thousands of defects. At the same time, the time and the effort for classifying the defects have remarkably increased. This increase in time and effort decreases a productivity of a semiconductor device. To prevent this decrease in the productivity of the semiconductor device, the inspection process is only performed on selected portions of the wafers. However, this selective inspection causes another problem in that a reliability of the inspection process may be lowered. Accordingly, a method and an apparatus for fast and efficient classification of defects are in demand.
FIG. 1 is a flow chart illustrating a conventional method for classifying defects of a wafer.
Referring to FIG. 1, in step S11, a surface of a wafer is scanned using defect inspecting equipment. In step S12, the defect inspecting equipment obtains information concerning the number and coordinates of defects generated on the wafer. In step S13, a server stores this information from the defect inspecting equipment.
In step S14, it is determined whether the number of defects exceeds a count specification. If the number of the defects on the wafer exceeds the count specification, a semiconductor fabricating process will be suspended due to a “spec out interlock” thereof. Subsequently, in step S15, the wafer is transferred to a review tool and is reviewed. Here, the review process represents a process that identifies the shape and formation of the defects on the wafer by an inspector using the review tool in accordance with the information concerning the defects. The review tool may be a microscope or a scanning electron microscope (SEM).
In step S16, the review process determines whether the extent to which defects on the wafer may affect the semiconductor manufacturing processes. In particular, it is determined whether the defects exceed a critical defect specification. If the defects on the wafer exceed the critical defect specification, in step S17, the semiconductor fabricating process is suspended due to a “spec out interlock” thereof.
If the number of defects fails to exceed the count specification in step S14 or the defects fail to exceed the critical defect specification in step S16, then, in step S18, subsequent semiconductor manufacturing processes are advanced.
FIGS. 2A and 2B are graphs illustrating results of a conventional method for classifying defects according to a manual review process.
Referring to FIG. 2A, when a number of defects detected exceeds a reference number, for example, about 200, the wafer is reviewed to determine whether further processes should be suspended or advanced.
In the review process, a worker, i.e., the inspector, visually inspects the defects on the wafer. The worker manually classifies the types of the defects, and then inputs the information concerning the classified defects onto a server, where the information is stored. Types of stored defects may be classified as shown in FIG. 2B. Specifically, a type I defect corresponds to a critical defect, from among type I to type IV defects. The number of type I defects may determine whether further processes are suspended or advanced. For example, type I defects indicate particles, type II defects represent flat defects, type III defects indicate contact recesses, and type IV defects represent scratches.
Since a conventional inspecting apparatus determines the review process in accordance with the total number of the defects on the wafer, the conventional inspecting apparatus may not discriminate between severity or types of the defects when the total number of the defects is below a reference number, even if all of the defects are of the most severe variety. As a practical matter, this often occurs in semiconductor manufacturing processes. Here, the reference number of the defects may be properly adjusted in the processes after the occurrence.
Particularly, when the number of the defects is in a range of about hundreds to thousands, a problem occurs in that not all of the defects may be classified because a time of the review process may be prohibitively long.
Furthermore, the classification of the defects through manual review may lack objectivity in view of the subjective judgment of the inspector. For example, the conventional inspecting apparatus inspects about 200 to about 300 wafers per day. The number of wafers inspected per day in one fabricating line using seven inspecting apparatuses is about 1,400 to about 2,100. Thus, only a small number of wafers are actually reviewed among the inspected wafers.
To overcome the problems caused by manual inspection, there is disclosed an auto defect classification (ADC). A method according to the ADC includes inspecting the defects on the wafer, determining coordinates of the defects, verifying images of the defects stored in the server and classifying the defects. The classification can be automatically performed in the ADC. However, the ADC may be practically employed in the present because the inspecting time of the ADC is much longer than that of the manual inspection and also initial conditions may not be easily set in the ADC.